1. Field of the Invention
The present invention relates to an illuminating optical apparatus and the making method thereof, an exposure apparatus and the making method thereof, and device manufacturing method. More specifically, the invention relates to an illuminating optical apparatus suitable for application to an exposure apparatus used in a lithographic process for manufacturing semiconductor devices or liquid crystal display devices (liquid crystal devices) and the making method of the optical apparatus, an exposure apparatus comprising this illuminating optical apparatus and a making method of the exposure apparatus, and a manufacturing method of devices using this exposure apparatus in the lithographic process. The illuminating optical apparatus of the invention is suitable for illuminating an object by the use of an energy beam having a short wavelength, for example, not longer than 300 nm.
2. Description of the Related Art
When forming fine patterns on electronic devices such as semiconductor devices (such as integrated circuits) and liquid crystal displays, conventionally, the patterns to be formed were proportionally enlarged four to five times on a photomask or a reticle (hereinafter collectively referred to as a xe2x80x9creticlexe2x80x9d), and then transferred onto a substrate to be exposed such as a wafer. The exposure was performed, in reduced magnification, with a reduction projection exposure apparatus such as a stepper.
With the projection exposure apparatus used for transferring such a pattern, the exposure wavelength has shifted to a smaller wavelength to cope with the tendency toward finer semiconductor integrated circuits. Currently, a wavelength of 248 nm in a KrF excimer laser is widely used, and the use of a shorter wavelength of 193 nm in an ArF excimer laser is becoming practical. Projection exposure apparatus employing a shorter wavelength of 157 nm in a F2 laser and 126 nm in an Ar2 laser are now being proposed.
Light with the wavelength from 120 to 200 nm is a vacuum ultraviolet light beam. Since a light flux within this wavelength band is poor in transmittance through an optical glass, materials for lenses and reticles capable of being used in a VUV exposure apparatus using vacuum ultraviolet (VUV) light for exposure are limited to crystals of fluorite, magnesium fluoride and lithium fluoride. Also, energy absorption by oxygen, water vapor or hydrocarbon gas (hereinafter from time to time referred to as xe2x80x9cabsorptive gasesxe2x80x9d) is extremely large. Therefore, it becomes necessary to alter the gas in the optical path portion with a gas which energy absorption of the exposure light is smaller (low-absorptive gas) in order to exclude oxygen from the optical path.
The amount of vacuum ultraviolet light beams absorbed by oxygen gas is very large. In order to avoid absorption by oxygen, therefore, it is necessary to limit the concentration of oxygen gas in the optical path so that it does not exceed 1 ppm of the average concentration of oxygen gas in the optical path. Particularly, in the illuminating optical system where the light illuminated from the light source proceeds to the reticle through the optical system, the total distance of the optical path is long, so the concentration of oxygen is required to be limited to a smaller value than described above.
FIG. 10 schematically illustrates an example of the illuminating optical system (illuminating optical unit) which configures a conventional exposure apparatus using an excimer laser beam.
This illuminating optical system shown in FIG. 10 comprises a first fly-eye lens system 202, a folded mirror 204, a second fly-eye lens system 206, an illuminating system diaphragm plate (diaphragm revolver) 208, a first relay lens system 210, a reticle blind 212, a second relay lens system 214, a folded mirror 216, and a condenser lens 218, sequentially arranged along the optical path of the exposure light in a predetermined positional relationship. The first fly-eye lens system 202 and the illuminating system diaphragm plate 208 are rotatably-driven by actuators 220 and 222. Movable blinds configuring the first relay lens system 210 and the reticle blind 212 are driven by actuators 224 and 226, respectively in predetermined directions. Sensors S1, S2, S3 and S4 for detecting the position or displacement are respectively provided on these movable portions. In this illuminating optical system, the above-mentioned optical members, the actuators and the sensors are in general, covered with a cover 230, and the interiors were purged with nitrogen (N2) gas, one of low-absorptive gases.
In this conventional illuminating optical system, the optical members configuring the illuminating optical system, the actuators, and the sensors are covered with a cover, therefore, the actuators and the sensors are located in the same space as the lenses and the mirrors. Consequently, adhesives, sealers and paints used for the actuators and the sensors, and gases emitted from these component members themselves have become the cause of chemical pollution sources of the optical devices such as lenses and mirrors.
In the above-mentioned conventional illuminating optical system, the shape of the cover has caused difficulty to completely cut off the air in the cover interior from open air outside the cover, and has allowed the chemically polluted open air containing oxygen to be mixed with the cover interior. This causes the problem of absorption of the illuminating light by the ozone generated from oxygen or photochemical reactions between oxygen and the illuminating light. Also, chemical pollution decreases the transmittance of the lenses and reflectivity of the mirrors, due to clouding substances adhered and deposited on the surfaces of the optical elements.
With an exposure apparatus, all these cases have caused a decrease in exposure accuracy resulting from a shortage in the amount of exposure light irradiated onto the wafer.
In the lithographic process for manufacturing semiconductor devices, conventionally, a stationary type exposure apparatus such as a reduction projection exposure apparatus (known as a stepper) employing a step-and-repeat method has been mainstream. However, along with the recent tendency toward a higher degree of integration of semiconductor devices and a larger wafer size, the scanning exposure apparatus employing a so-called slit scanning method and the step-and-scan method are becoming more popular. With these apparatus, a rectangular or arcuated illuminating areas on a reticle having a pattern formed are illuminated with an illuminating light, and the reticle and substrate such as a wafer are synchronously moved in a linear direction, thereby sequentially transferring the pattern onto the substrate.
With this apparatus, a movable blade (also called a xe2x80x9cmovable blindxe2x80x9d) is arranged for limiting the illuminating area on the reticle so as to avoid unnecessary exposure of a portion outside the pattern area on the reticle during exposure. This blind is a movable member, which moves during exposure. It has been arranged in the illuminating optical system, which illuminates the reticle R by an illuminating light from a light source, and is driven synchronously with the reticle during exposure (refer to Japan Patent Laid Open No. 04-196513 and the corresponding U.S. Pat. No. 5,473,410).
Semiconductor devices are formed, by depositing multiple layers of circuit patterns with respect to one another in a predetermined positional relationship onto a wafer. For this reason, in an exposure apparatus used for manufacturing semiconductor devices or the like, it is necessary to accurately overlay the patterns formed on the reticle and conduct transferring.
In the conventional scanning type exposure apparatus, however, as described above, in the illuminating optical system the movable member is arranged and moves during exposure, causing vibration in the illuminating optical system. This, in turn, causes an adverse effect on the main portion of the exposure apparatus in which the illuminating optical system is incorporated. The main portion of the exposure apparatus include a reticle stage holding the reticle R, a projection optical system projecting the pattern of the reticle R onto the wafer, and a wafer stage holding the wafer. It also includes a main portion column holding the reticle stage, projection optical system, wafer stage and the illuminating optical system, and a laser interferometer is arranged on the main portion column for measuring the positions of the both stages. The vibration described above in the illuminating optical system during exposure, especially, the residual vibration during exposure, affects the accuracy of synchronous movement between the reticle stage and the wafer stage. It also affects the positional relationship between the projection optical system and the two stages, and the values measured by the interferometer, resulting in reducing the exposure accuracy of the scanning type exposure apparatus.
If there is vibration in the illuminating optical system during exposure, the vibration similarly affects the exposure accuracy also in the stationary exposure apparatus employing the step-and-repeat method.
The present invention was developed in view of the circumstances as described above, and has a first object to provide an illuminating optical apparatus, which improves the degree of chemical cleanliness of the interior thereof.
A second object of the invention is to provide an exposure apparatus, which improves the exposure accuracy.
A third object of the invention is to provide a device manufacturing method, which improves the productivity of high-integrity microdevices.
According to a first aspect of the invention, there is provided an illuminating optical apparatus to illuminate an object with an energy beam from a light source, comprising at least one of a first optical unit which includes at least one of a drivable first optical member, and a first frame holding the first optical member, at least one of a second optical unit which has at least one of a second optical member of which a movable amount is smaller than a movable amount of the first optical member, and a second frame holding the second optical member, and a first connecting member which displaceably connects the first frame in respect to the second frame.
The expression xe2x80x9ca movable amount smaller than the movable amount of the first optical memberxe2x80x9d is a concept covering a movable amount of null. Accordingly, the second optical unit may comprise only a non-movable optical member as the optical member.
According to the above, the frame structuring the first optical unit which has the first optical member being drivable, and the frame structuring the second optical unit which has the second optical member having a movable amount smaller than the movable amount of the first optical member, are displaceably connected via the first connecting member in respect to each other. As described above, in between frames requiring respective displacement to some extent, first connecting member suitable for the purpose is used. This improves air-tightness in the space within the frame and the space in between adjacent frames. Therefore, in the illuminating optical apparatus of the present invention, air-tightness is improved upon purging the low-absorptive gas such as nitrogen gas in the internal space of the frame and the space in between the adjacent frames, making it possible to improve the degree of chemical cleanliness in the interior space. The optical units having the frames can be easily replaced, since it is possible to separate the frames by simply removing the first connecting member.
In this case, for example, the first connecting member can be a freely expansible bellows-shaped member of which an inner surface is chemically cleaned. The chemical cleaning process may be, for example, the bellows-shaped member having an inner surface coated with fluoropolymers.
Or, the first connecting member may comprise a secondary vulcanized fluororubber. The secondary vulcanized fluororubber, which is in itself, a chemically clean material, may be used as a material for the first connecting member.
In the first illuminating optical apparatus of the present invention, a plurality of the second optical units are provided, and may further comprise a second connecting member which connects the second frame so as to suppress a displacement among the second frames. The second frames structure a part of the second optical units. In such a case, as described above, the frame configuring the first optical unit and the frame configuring the second optical unit are connected relatively displaceably via the first connecting member, while the frames configuring the second optical unit are connected (fixed) to each other via the second connecting member so as to suppress relative displacement. Frames which requiring relative displacement to some extent, and frames not requiring relative displacement are connected via different connecting members respectively suitable, thus improving air-tightness of the space interior of the frames and the space in between thereof.
In this case, for example, the second connecting member can be an O-ring which has at least a surface chemically cleaned. In this case, similar to the case above, the O-ring can comprise a resin, and can have the surface coated with fluoropolymers.
Or, the second connecting member, for example the, O-ring, may comprise a secondary vulcanized fluororubber. That is, as the material of the second connecting member, for example, the O-ring, a secondary vulcanized fluororubber, which is a chemically clean material, may be used.
Furthermore, the second connecting member may be an O-ring formed of a tube. In such a case, the O-ring becomes easily crushable by providing a larger crushing margin of the O-ring, thus improving operability of the connecting operation between frames using the O-ring.
The first illuminating optical apparatus of the present invention may further comprise an actuator which is arranged outside the first frame, and drives the first optical member held by the frame. In such a case, since the actuator is arranged outside the frame holding the drivable first optical member, the actuator is not the source of pollution for the frame and its interior, thus reducing the degree of the optical elements to be clouded by the pollution.
According to a second aspect of the invention, there is provided an illuminating optical apparatus to illuminate an object with an energy beam from a light source, comprising: a plurality of optical members arranged in a predetermined positional relationship, at least one of the plurality of optical members is a movable member; and an illuminating system housing disposed around the plurality of optical members to house the plurality of optical members to isolate the interiors thereof from the open air; an actuator which is arranged outside the illuminating system housing, and respectively drives the movable member; and a sensor which is arranged on the outside of the illuminating system housing, and measures a position or a displacement of at least one of the movable members.
With this apparatus, actuators for driving the movable members, respectively, are arranged outside the illuminating system housing containing at least a movable members, housing a plurality of optical members arranged in a predetermined positional relationship, and keeping the interiors thereof isolated from the open air in an sealed state. The actuators, therefore, are not the source of pollution for the interior of the illuminating system housing. So, in the second illuminating optical apparatus of the present invention, the degree of chemical cleanliness in the interior can be improved by purging a low-absorption gas such as nitrogen gas in the illuminating system housing, since the actuators do not act as a pollution source.
In this case, as with the actuators, the sensors are not the source of pollution in the interior of the illuminating system housing. The sensors, therefore, do not cause a decrease in the degree of chemical cleanliness in the illuminating system housing, and furthermore can control the actuators at a high accuracy based on the sensor output, allowing highly accurate positional control of the drivable optical member.
With the second illuminating optical apparatus of the invention, it is preferable that at least one of the movable members is a rotatable member which rotates around a predetermined rotation shaft, and a bearing section which supports the rotation shaft arranged in the illuminating system housing, and a magnetic fluid seal is provided between the bearing section and the rotation shaft. In this case, a magnetic liquid serving as lubricant oil enters in to a gap between the rotation shaft and the bearing. The air-tightness of the bearing section can be improved, as well as smoothing the rotation of the rotation shaft.
In this case, a fluorine contained oil may be used for the magnetic fluid seal. By using the fluorine contained oil which is a chemically clean substance, it is possible to suppress a decrease in the degree of chemical cleanliness.
According to a third aspect of the invention, there is provided an exposure apparatus for transferring a mask pattern onto a substrate, comprising an illuminating optical apparatus of the present invention, which illuminates the mask with an energy beam.
With this exposure apparatus, since the first illuminating optical apparatus of the present invention is used as an illuminating apparatus for illuminating a mask by an energy beam, it is possible to improve chemical cleanliness of the interior of the illuminating optical apparatus. This can effectively suppress the decrease in transmittance of optical elements in the illuminating optical apparatus, even when using an energy-beam for exposure having a wavelength of not longer than 300 nm. Accordingly, it is possible to prevent a decrease in the amount of exposure light irradiated onto the substrate surface, so as to achieve a highly accurate (high-resolution) exposure by the short-wave energy beam, as well as improve the throughput by shortening the exposure time.
According to a fourth aspect of the invention there is provided a second exposure apparatus of transferring a mask pattern onto a substrate, comprising a second illuminating optical apparatus which illuminates the mask with an energy beam.
With this exposure apparatus, the second illuminating optical apparatus of the present invention is used as an illuminating apparatus illuminating a mask by an energy beam. This makes it possible to improve the degree of chemical cleanliness of the interior of the illuminating optical apparatus. As a result, even when using an energy beam for exposure having a wavelength not longer than 300 nm, it is possible to effectively prevent a decrease in transmittance of the optical elements in the illuminating optical apparatus. The decrease in the amount of exposure light irradiated onto the substrate surface can also be suppressed, so as to achieve a highly accurate (high-resolution) exposure by the short-wave energy beam, as well as improve the throughput by shortening the exposure time.
According to a fifth aspect of the invention, there is provided an exposure apparatus of transferring a mask pattern onto a substrate by exposing the substrate with the energy beam via the mask, comprising: an illuminating optical system which has a first illuminating system housing which isolates a first partial optical system containing a first movable section which is movable during exposure from open air and keeps the first partial optical system in a sealed state, and a second illuminating system housing which isolates a second partial optical system physically separated from the first partial optical system containing an optical member of which the movable amount during the exposure is smaller than the movable amount of the first movable section from the open air and keeps the second partial optical system in the sealed state; and a main portion for exposure on which the second illuminating system housing is provided, including at least a substrate stage which holds the substrate exposed by the energy beam outgoing the mask; a connecting section which isolates from the open air a space between the first illuminating system housing and the second illuminating system housing and keeps the space in a sealed state, and connects the first illuminating system housing and the second illuminating system housing so as to limit the amount of vibration which travels between the two housings.
With this exposure apparatus, the illuminating optical system has a first illuminating system housing which comprises a first partial optical system with a first movable section which is movable during exposure isolated and kept sealed from the open air. The exposure apparatus also has a second illuminating system housing which comprises a second partial optical system physically separate from the first partial optical system and which has only optical members with a movable amount during exposure smaller than the movable amount of the first movable section (that is, does not contain optical members having a movable amount of over that of the first movable section), and isolates and keeps sealed. That is, the first partial optical system and the second partial optical system each have illuminating system housings to isolate the interior from the open air, so as to prevent the open air to mix with the interior and become the source of pollution. The second illuminating system housing is installed in the main portion for exposure containing at least a substrate stage holding the substrate exposed by the energy beam emitted from the mask. As a result, even when the first movable section moves largely during exposure causing vibration in the first illuminating optical system and residual vibration remains during exposure, the second partial optical system and the main portion for exposure incorporating the second partial optical system is almost free from the adverse effect of vibration. Furthermore, the connecting section connects the first illuminating system housing configuring the first partial optical system and the second illuminating system housing configuring the second partial optical system by isolating the space between them from the open air into an air-tight condition. Therefore, it is possible to prevent the open air from flowing into the space between the first illuminating system housing and the second illuminating system housing, and from becoming a pollution source. The connecting section also connects the first illuminating system housing and the second illuminating system housing while limiting the transfer of vibration between the two systems. So even if the vibration of the first illuminating system housing during exposure is transferred to the second illuminating system housing and the main portion for exposure, it hardly affects the accuracy of exposure.
According to the third exposure apparatus of the invention, therefore, it is possible to alleviate the effect of vibration of the illuminating optical system during exposure on the exposure main portion, and consequently to improve exposure accuracy.
Accordingly, the third exposure apparatus of the present invention can reduce the vibration caused by the illuminating optical system during exposure, while effectively preventing the open air to mix into the illuminating path, and as a result improving the accuracy of exposure.
In this case, the second partial optical system may comprise optical members that are stationary during the exposure, i.e., non-movable optical members, or optical members movable (displaceable) only during the non-exposure state, or the second partial optical system may include a second movable section movable in an amount smaller than that of the first movable section during exposure. Even in the latter case, vibration of the second partial optical system and the main portion of exposure during exposure is obviously reduced compared with vibration of the conventional exposure apparatus, in which residual vibration of the first partial optical system had been directly transferred to the second partial optical system and the exposure main portion.
In the third exposure apparatus of the present invention, nitrogen (N2) gas or helium (He) gas having an oxygen mixture of less than a predetermined value, or preferably less than 1 ppm may be purged as a low-absorptive gas into the illuminating system housings. In such a case, it is possible to suppress absorption of the energy beam by an absorptive gas (oxygen, water vapor, hydrocarbon gas) in the first partial optical system and the second partial optical system. Accordingly, for example, an energy beam having a wavelength not longer than 300 nm (such as KrF excimer laser beam having a wavelength of 248 nm, ArF excimer laser beam having a wavelength of 193 nm, or the like) may be used. Even with the usage of such energy beams, it is possible to perform an exposure (transfer of a mask pattern onto the substrate) with high accuracy.
The third exposure apparatus of the present invention, a low-absorptive gas may be purged into the space between the first and second illuminating system housings and the interiors of the respective illuminating system housings. In such a case, the low-absorptive gas is purged in the space between the first and second illuminating system housings and the interiors of these illuminating system housings, therefore, a chemically clean state can be maintained. The energy beam can be a vacuum ultraviolet light beam, and a wavelength thereof is not longer than 200 nm (for example, F2 laser beam having a wavelength of 157 nm, Kr2 laser beam having a wavelength of 146 nm, or Ar2 laser beam having a wavelength of 126 nm). Since it is possible to suppress absorption of the energy beam by the absorptive gas in the space between the first and second illuminating system housings and the interiors of these illuminating system housings, exposure of a higher accuracy can be performed by using an energy beam of the vacuum ultraviolet region.
In the third exposure apparatus of the invention, the connecting section which isolates the space between the first illuminating system housing and the second illuminating system housing into a sealed state, and connects the first illuminating system housing and the second illuminating system housing while limiting transfer of vibration between these housings may comprise, for example, an expansible bellows-shaped member.
In the third exposure apparatus of the invention, the first partial optical system may include: an optical integrator, and a diaphragm plate of the illuminating system having at least one of a diaphragm arranged near an emitting surface of the optical integrator, and an iris diaphragm; and the first movable section further has a switching unit which positions at least one of diaphragm and the iris diaphragm, on the emitting surface of the optical integrator.
In the third exposure apparatus of the present invention, the first movable section may be a movable blade, which limits the irradiation area on the mask during exposure with the energy beam.
According to a sixth aspect of the invention, there is provided a method of making an exposure apparatus for transferring a mask pattern onto a substrate by exposing the substrate with the energy beam via the mask, comprising: providing a main portion of exposure with a substrate stage incorporated, the substrate stage holding the substrate; providing a first illuminating system housing which isolates a first partial optical system containing a first movable section which is movable during exposure from open air and keeps the first partial optical system in a sealed state; and installing a second illuminating system housing which isolates a second partial optical system physically separated from the first partial optical system containing an optical member of which the movable amount during exposure is smaller than the movable amount of the first movable section from the open air and keeps the second partial optical system in the sealed state, to the main portion for exposure; and connecting the first illuminating system housing and the second illuminating system housing so as to limit the amount of vibration which travels between the two housings by a connecting section, and isolate from the open air a space between the first illuminating system housing and the second illuminating system housing and keeps the space in a sealed state.
According to the seventh aspect of the present invention, there is provided a making method of an illuminating optical apparatus to illuminate an object with an energy beam from a light source, which comprises: providing at least one of a first optical unit which includes at least one of a drivable first optical member; and a first frame holding the first optical member, providing at least one of a second optical unit which has at least one of a second optical member of which a movable amount is smaller than a movable amount of the first optical member, and a second frame holding the second optical member; and connecting the first frame structuring the first optical unit and the second frame structuring the second optical unit with a first connecting member which displaceably connects the first frame in respect to the second frame.
In the lithographic process, by using the first, second and third exposure apparatus of the present invention, a pattern can be formed on the substrate with high accuracy, and hence high-integrity microdevices can be manufactured at a satisfactory yield. Therefore, according to still another aspect of the invention, there is provided a device manufacturing method using any of the first to third exposure apparatuses of the invention.